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United States Patent |
5,200,950
|
Foglar
,   et al.
|
April 6, 1993
|
Method and circuit arrangement for reducing the loss of message packets
that are transmitted via a packet switching equipment
Abstract
In order to reduce the loss of message packets that are transmitted in the
course of virtual connections in an asynchronous transfer mode and which
comprise a packet header identifying the respective virtual connection,
the message packets being respectively augmented by a continuous auxiliary
identifier and, after multiplication, being separately transmitted via
redundant switching matrices of a packet switching equipment, it is
provided that, with reference to the auxiliary identifier, only that
message packet transmitted without fault as a first of the multiplied
message packets and having an auxiliary identifier that is the next one
following the most recently-transmitted message packet is forwarded. In
addition, that switching matrix by way of which the transmission of
message packets respectively occurs most slowly is identified and message
packets that are transmitted via the respective slowest switching matrix
as the first of the multiplied message packets are forwarded.
Inventors:
|
Foglar; Andreas (Munich, DE);
Rau; Peter (Munich, DE)
|
Assignee:
|
Siemens Aktiengesellschaft (Munich, DE)
|
Appl. No.:
|
690360 |
Filed:
|
April 24, 1991 |
Foreign Application Priority Data
| Apr 27, 1990[EP] | 90108055.6 |
Current U.S. Class: |
370/219; 370/244; 370/399 |
Intern'l Class: |
H04L 001/22 |
Field of Search: |
370/58.1,58.2,58.3,60,60.1,94.1,94.2,16,13
371/8.1,8.2,11.1,11.2
|
References Cited
U.S. Patent Documents
4455645 | Jun., 1984 | Mijioka et al. | 370/16.
|
4730303 | Mar., 1988 | Suzuki | 370/60.
|
5084867 | Jan., 1992 | Tachibana et al. | 370/16.
|
Foreign Patent Documents |
0108555 | May., 1984 | EP.
| |
0321050 | Dec., 1987 | EP.
| |
Other References
Schneider H., "Mit ATM . . . Kommunikation", Telcom Report, vol. 13, No. 1,
1990, pp. 4-7.
Newman P., "A Broad-Band . . . Communications", IEEE Infocom '88, New York,
1988, pp. 0019-0028.
|
Primary Examiner: Olms; Douglas W.
Assistant Examiner: Chin; Wellington
Attorney, Agent or Firm: Hill, Steadman & Simpson
Claims
We claim:
1. In a method for forwarding message packets transmitted from offering
trunks onto serving lines via virtual connections during asynchronous
transmission of said message packets, each message packet having a packet
header which identifies a respective virtual connection through packet
switching equipment comprising a plurality of redundant switching
matrices, in which a message packet group having a plurality of identical
message packets corresponding in number to the number of redundant
switching matrices is formed by duplication of each of the message packets
transmitted on one of the offering trunks in the course of a virtual
connection, in which an identical auxiliary identifier, which is changed
for each of the successive message packet groups, is attached to each
message packet of a message packet group, in which the message packets of
a message packet group are separately transmitted across the redundant
switching matrices in the direction of the serving lines defined by
respective virtual connections, and in which only one of the message
packets of a message packet group is forwarded to the serving line defined
by the virtual connection after such a transmission across the redundant
switching matrices on the basis of the auxiliary identifier respectively
attached to the message packets, the improvement wherein:
after the separate transmission of the message packets of one of said
message packet groups respectively across the redundant switching matrices
towards the defined serving line and checking for transmission faults,
forwarding a first-arriving faultlessly-transmitted message packet of said
one message packet group whose message packets have the auxiliary
identifier that is the next following the auxiliary identifier of the most
recently-transmitted message packet;
identifying one of said plurality switching matrices via which the
transmission of the message packets occurs the slowest; and
forwarding to the defined serving line the message packets that ar
faultlessly transmitted as the first of their respective message packet
group via said slowest switching matrix.
2. The improved method of claim 1, and further defined by:
in the course of setting up a virtual connection,
setting an average counter reading for each of the redundant switching
matrices of the packet switching equipment;
incrementing the counter reading of the switching matrix, via which the
message packet just forwarded to the defined serving line was transmitted,
by a value that corresponds to the number of redundant switching matrices
reduced by one; and
decrementing the counter reading of the switching matrices that have not
transmitted the message packet currently being forwarded by a value one,
whereby, the switching matrix having the lowest counter reading for the
respective virtual connection is identified as the respective slowest
switching matrix.
3. The improved method of claim 2, and further defined by:
triggering a malfunction alarm when a counter reading of a switching matrix
that has not transmitted a plurality of forwarded message packets reaches
a count which can be defined by zero.
4. The improved method of claim 3, and further defined by:
when all counter readings except one have the highest or lowest counter
reading that identifies a switching matrix by way of which no message
packet was forwarded to the serving line for a predetermined time
interval, forwarding each faultlessly-transmitted message packet that
follows the most recently-forwarded message packet via the switching
matrix associated with that one counter reading.
5. In a circuit arrangement of the type for forwarding message packets
transmitted on offering trunks in the course of virtual connections and
onto serving lines during asynchronous transmission of message packets, in
which each message packet has a header that identifies the respective
virtual connection, via a packet switching equipment comprising at least
two redundant switching matrices, in which each of the offering lines is
connected to each of the switching matrices by a respective handling
device which forms message packet groups of identical message packets and
attaches a auxiliary identifier to each message packet, which auxiliary
identifier is changed for each message packet group, the number of
identical message packets of a message packet group corresponding to the
number of redundant switching matrices, in which a plurality of evaluation
devices connect each of the redundant switching matrices to each of the
serving lines, each of said evaluation devices accepting message packets
transmitted via the redundant switching matrices and, on the basis of the
auxiliary identifier attached to the message packets and the auxiliary
identifier just used by a handling device in the formation of a message
packet group for a respective virtual connection, outputs only one of the
message packets of a message packet group to an allocated serving line,
the improvement therein comprising:
forwarding means in each of said evaluation devices for forwarding to the
respective serving line the message packet of a message packet group that
arrives first with an auxiliary identifier that follows the auxiliary
identifier of the most recently-transmitted message packet; and
identification means in each of said evaluation means for identifying the
redundant switching matrix by which the transmission of message packets
occurs the slowest and for forwarding to said serving line those message
packets which are the first message packets of their message packet group
to have been faultlessly transmitted via said slowest switching matrix.
6. The improved circuit arrangement of claim 5, wherein each of said
evaluation devices comprises:
a memory including a plurality of memory locations for storing the
respective auxiliary identifier that is current for the evaluation of a
message packet group for the individual virtual connections, the memory
locations being respectively selectable in response to the contents of the
packet headers of the message packets that identify the respective virtual
connections; and
updating means responsive to each selection of a memory location to up date
the auxiliary identifiers stored in the memory locations.
7. The improved circuit arrangement of claim 6, wherein each of said
evaluation devices comprises:
means for storing, in addition to a respective current auxiliary
identifier, a respective information in the respective memory location
identifying the slowest switching matrix for the virtual connection.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is related to an application Ser. No. 678,046 filed Apr.
1, 1991.
1. Field of the Invention
The present invention relates to a method and to an apparatus for
forwarding cells, that are referred to below as message packet transmitted
on offering trunks in the course of virtual connections in an asynchronous
transfer mode.
2. Description of the Prior Art
It is generally known in the art, through the European patent application
89 103 798.8 to provide a method and apparatus for forwardly message
packets transmitted on offering trunks in the course of virtual
connections in an asynchronous transfer mode in which the packets have a
packet header that identifies the respective virtual connection via a
packet switching equipment which comprises at least two redundant
switching matrices feeding serving lines, whereby a message packet group
having a plurality of identical message packets corresponding in number to
the plurality of redundant switching matrices is formed by multiplication
of each of the message packets transmitted on one of the offering trunks
in the course of a virtual connection. An identical auxiliary identifier
that changes for successive message packet groups is attached to each of
the message packets of a message packet group and the message packets of a
message packet group are separately transmitted across the redundant
switching matrices in the direction of the serving line coming into
consideration for the respective virtual connection. Only one of the
message packets belonging to a message packet group is forwarded to the
serving line coming into consideration after such a transmission across
the redundant switching matrices, the message packet being forwarded on
the basis of the auxiliary identifier respectively attached to the message
packets.
As mentioned above, such a method and circuit arrangement have already been
disclosed in the European patent application 89 103 798.8.
Given a faulty transmission of a message packet in this method or by way of
this circuit arrangement, a loss of an entire message packet cycle can
occur that can cover, for example, a plurality of 64 message packets.
SUMMARY OF THE INVENTION
The object of the present invention, therefore, is to provide a method and
an apparatus of the type generally set forth above that reduces the
possible loss of message packets.
In a method of the type generally set forth above, the aforementioned
object is achieved, according to the present invention, in that, after the
separate transmission of the message packets of a message packet group
across the redundant switching matrices, the first,
faultlessly-transmitted message packet to arrive in a message packet group
whose message packets have the auxiliary identifier that is the next
following the auxiliary identifier of the most-recently transmitted
message packet is forwarded to the serving line coming into consideration
and/or in that the switching matrix by way of which the transmission of
the message packet occurs most slowly is identified and that the message
packets that are faultlessly transmitted as the respective first of their
message packet group via the respective, slowest switching matrix, are
forwarded to the serving line coming into consideration. This method
yields the advantage that the loss of a plurality of message packets
corresponding to a message packet cycle that, for example, can cover a
plurality of 64 message packets, need not be accepted in case of the
absence of the message packet having the auxiliary identifier that is the
next to follow the message packet that was most-recently transmitted;
rather, on the contrary, the first faultlessly-transmitted message packet
of each message packet group is forwarded regardless of its auxiliary
identifier.
According to a further development and feature of the invention, the
respective slowest matrix is identified by a respective virtual connection
in that, in the course of the set-up of a virtual connection, an average
counter reading is set for each switching matrix provided in the packet
switching equipment and in that the appertaining counter reading of the
switching matrix by way of which the message packet just forwarded to the
appertaining serving line was transmitted is incremented by the value that
corresponds to the plurality of switching matrices provided in the packet
switching equipment, reduced by 1, and, accompanying this, the counter
reading of the switching matrices that have not transmitted the message
packet now being forwarded are deincremented by a value 1 whereby a
switching matrix whose counter reading has the respective lowest counter
reading for the respective virtual connection is a respective, slowest
switching matrix.
This measure yields the advantage that a respectively slowest switching
matrix or a plurality of transmitted message packets can be identified for
each virtual connection in a particularly simple manner, whereby arbitrary
scatters in the transmission speed of the switching matrices are
compensated.
It can be provided in a further development and in accordance with a
further feature of the invention that a malfunction alarm is triggered
when a counter reaches a counter reading during the course of a connection
that identifies a switching matrix that, itself, has not transmitted a
plurality of forwarded message packets. This measure yields the advantage
of a possibility of fault detection that is particularly low in expense.
According to a further development and feature of the invention, it can be
provided that, when all counters except one have the highest, or
respectively, lowest counter reading that respectively identifies a
switching matrix via which no message packet was forwarded for the serving
line for a longer time interval, each faultlessly-transmitted message
packet that follows the most-recently forwarded message packet is
forwarded via the switching matrix belonging to the respective, one
counter.
This measure yields the advantage that, given outage of the redundant
transmission paths of a virtual connection, each faultlessly-transmitted
message packet is forwarded to the appertaining serving line via the
switching matrix that is the only one considered capable of transmission.
A circuit arrangement for the implementation of the method of the type set
forth above, comprises a handling device for each offering trunk and an
evaluation device for each serving line, whereby such a circuit
arrangement is characterized, according to the present invention, in that
the respective evaluation device respectively forwards that message packet
of a message packet group to the allocated output line that arrives first
with a auxiliary identifier that follows the auxiliary identifier
most-recently transmitted message packet. The evaluation device
respectively identifies that switching matrix by way of which the
transmission of message packets occurs most slowly and in that the
evaluation device forwards message packets that, as the respectively first
message packet of their message packet group, are faultlessly transmitted
via the respective slowest switching matrix.
The circuit arrangement for the implementation of the method of the present
invention yields the advantage of a low circuit-oriented expense for the
forwarding of the message packets via the redundantly-designed packet
switching equipment.
According to the invention, a circuit arrangement for forwarding message
packets transmitted on offering trunks in the course of virtual
connections in an asynchronous transfer mode and that have a packet header
that identifies the respective virtual connection via a packet switching
equipment comprising at least two redundant switching matrices to feed
onto serving lines is provided in which each of the offering trunks has a
handling device allocated thereto which, first of all, attaches a
respective auxiliary identifier that changes for successive message
packets-to-message packets transmitted via the respective offering trunk
and, secondly, for a respective message packet group of the message
packets augmented by the auxiliary identifier and, having a plurality of
identical message packets corresponding in number to the plurality of
redundant switching matrices which are supplied to the redundant switching
matrices, each of the serving lines has an evaluation device allocated
thereto which accepts message packets transmitted via the redundant
switching matrices and, on the basis of the auxiliary identifier
respectively attached to the message packets and, potentially, on the
basis of the auxiliary identifier available and just used by the handling
device in the formation of a message packet group for the respective
virtual connection, outputs only one of the message packets belonging to a
message packet group to the allocated serving line.
The circuit arrangement is particularly characterized in that the
respective evaluation device forwards that message packet of a message
packet group to the allocated output line that arrives first with a
auxiliary identifier that follows the auxiliary identifier of the
most-recently transmitted message packet, and that the evaluation device
respectively identifies that switching matrix by way of which the
transmission of message packets occurs most slowly and in that the
evaluation device forwards message packets that, as the respective first
message packet of their message packet group, are faultlessly transmitted
via the respective slowest switching matrix.
According to another feature of the invention, the above circuit
arrangement is particularly characterized in that a memory having a
plurality of memory locations is provided in the evaluation device,
respectively, in which memory locations the auxiliary identifier that is
now current for the evaluation of the message packet group is individually
stored for the individual virtual connections; and in that the memory
locations are respectively selectable for an offering of the storage
auxiliary identifier on the basis of particulars respectively contained in
the packet header of the message packets and that identify the respective
virtual connection, and in that the auxiliary identifier stored in a
memory location is updated in response to each selection of a memory
location.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invention, its organization,
construction and operation will be best understood from the following
detailed description, taken in conjunction with the accompanying drawings,
on which:
FIG. 1 is a block circuit diagram of a packet switching equipment employing
the techniques of the present invention; and
FIG. 2 is a block diagram of a possible structure of an evaluation device
in which the method of the present invention is realized and that is only
schematically illustrated in single block form in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 schematically illustrates a packet switching system PVE to which a
plurality of offering trunks E1-En, as well as a plurality of serving
lines A1-An are connected. Of these, only the offering trunks E1 and En
and the serving lines A1 and An are illustrated in FIG. 1. A respective
transmission of message packets in the course of virtual connections
according to an asynchronous transfer mode occurs on the offering trunks
and serving lines. It is assumed that the message packets be packets
having a fixed length that each have a packet header with a respective,
virtual channel number as well as an information portion. The respective
virtual channel number, here referenced VCI, defines, in accordance with
the virtual connection, that serving line to which the respective message
packet is to be transmitted. The transmission of the actual message signal
occurs in the information portion. As used herein message signals are data
and text signals as well as voice or picture signals in digital form. It
can also be provided that a check information that is formed with a
preceding signal state sequence of the message packet, is attached each of
to the message packets.
As proceeds from FIG. 1, a handling device BHE is allocated to each of the
offering trunks E1-En. This handling device BHE that, for example, can be
represented by a handling device disclosed in the European application 89
103 798.8, corresponding to U.S. Ser. No. 487,220, fully incorporated
herein by this reference attaches a auxiliary identifier to message
packets belonging to a virtual connection, this auxiliary identifier
changing for successive message packets of the respective virtual
connection. The auxiliary identifier is composed of a sequence number that
is individually set to a defined initial value during the course of the
call set up for each virtual connection and that is incremented for each
successive message packet. For example, a plurality of 64 successive
message packets can form a message packet cycle. The sequence number can
then preferably assume a number of states that corresponds to the number
of message packets that a message packet cycle covers. The handling device
BHE forms two identical message packets from the incoming message packets,
each augmented with the auxiliary identifier, these identical message
packets being referred to below as message packet groups, and forwards
these message packets to two redundant matrices KV1 and KV2 of the message
packet switching equipment PVE. It is schematically indicated in FIG. 1
with reference to the switching matrix KV1 that the two switching matrices
KV are respectively assumed to comprise a plurality of switch modules SN
connected to one another. Since the structure and operation of such
switching matrices KV are already well known in the art, the same shall
only be discussed below with respect to the operation of a structure for
the present invention.
Each of the switching matrices KV comprises a plurality of output lines
L11-L1m, L21-L2m. One output line L1 of the switching matrix KV1 and one
output line L2 of the switching matrix KV2 are thereby connected in common
to a separate evaluation device AWE. These evaluation devices AWE are
connected to respective ones of the serving lines A1-An. Such an
evaluation device accepts the message packets transmitted via the two
switching matrices KV and, on the basis of an evaluation of the auxiliary
identifier respectively attached to the message packets and that shall be
set forth in greater detail below, outputs only one of the message packets
belonging to a message packet group to the allocated serving line A.
It should also be pointed out with respect to the packet switching
equipment PVE under consideration that this, in fact, has two redundant
switching matrices according to FIG. 1. The number of redundant switching
matrices, however, can also be correspondingly increased dependent on the
outage possibility of each of the switching matrices KV and on the
required values for the availability of the packet switching equipment
PVE.
FIG. 2 sets forth a possible structure of the evaluation device AWE
illustrated in FIG. 1. The message packet of a message packet group
transmitted via the respective output lines L1, L2 first traverse
interface devices respectively referenced S1 and S2. The recognition of a
beginning of a message packet and the synchronization of the received
message packets with the system clock with which the evaluation device AWE
is driven respectively occur in the interface devices. A respective check
of the transmitted message packets in view of a faultless transmission
also occurs in these interface devices, whereby a check with reference to
the check information can be added when a respective check information is
attached to the message packets. When such a faultless transmission is
present, then the interface device S1 delivers the message packet just
checked to an intermediate register ZR1. Given a faultless transmission,
the interface device S2 supplies the message packet just checked to an
intermediate register ZR2 in a corresponding manner. For each
faultlessly-transmitted message packet, the packet header, that comprises
a channel number VCI belonging to the respective virtual connection and a
sequence number that is continuously assigned by the input-side handling
device BHE of the packet switching equipment PVE, is additionally supplied
to a selection circuit AS. The respective packet header is supplied by the
selection circuit AS to a control device MP that can be formed, for
example, with a microprocessor and that, as indicated by the broken-line
arrow, is connected to a higher-ranking controller (not shown) of the
packet switching equipment PVE. The virtual channel number VCI contained
in the respective packet header is supplied to a memory SP and, therein,
serves the purpose of addressing a plurality of memory locations wherein,
among other things, the call-associated sequence number that is set to a
defined initial value during the course of the set up of the respective
virtual connection is deposited. The memory content of the
respectively-addressed memory locations is transferred to the control
device MP. A check is carried out in the control device MP to see whether
the sequence number supplied by the selection circuit AS is the next
sequence number following the most-recently forwarded message packet.
Given a positive result, the control device MP, with reference to an
auxiliary information W supplied along with the packet header from the
selection circuit AS that indicates which switching matrix KV had
transmitted the respective message packet, effects the forwarding of the
respective message packet from the appertaining intermediate register ZR
into a buffer memory PSP that, in a sequence of their input, forwards the
accepted message packets to the serving line A that is connected to the
respective evaluation unit AWE. This effects a matching of the
transmission speed prevailing within the packet switching equipment PVE to
the transmission speed of the respective serving line A that is lower in
comparison thereto. During this forwarding, the individual message packets
pass through a converter CONV in which the auxiliary identifier attached
to the message packets in the handling device BHE of the input side is
removed. The respective sequence number located in the control device MP
and belonging to the message packet being transmitted is stored in the
call-associated memory locations; the respective sequence number can
thereby be incremented, as a result whereof the identification of the
next-successive message packet is limited to a comparison of the
respective sequence numbers. In this procedure, a message packet is the
respective next message packet following the most-recently forwarded
message packet, wherein a comparison of the sequence number carried by the
message packet just being transmitted to the sequence number that was
most-recently deposited in the memory SP for the virtual connection yields
coincidence.
Message packets that are respectively intermediately stored in the
intermediate register ZR and that are not forwarded by the control device
MP are overwritten by the respective next message packet input into the
intermediate register ZR. For each message packet forwarded out of the
intermediate register ZR, the sequence number corresponding to the
respective transmitted message packet that, for example, can be
represented by the incremented sequence number carried in the packet
header of the respective message packet is stored in the memory SP with
the virtual channel number VCI as an address. In addition to the
respective sequence number, the information here referenced W, a plurality
of counter readings here referenced Z and an information reference V are
stored in a call-associated manner in the memory SP.
A respective switching matrix KV via which the transmission of message
packets respectively occurs most slowly can be identified with the
assistance of the counter readings Z. During the course of the set up of a
connection, the appertaining counter readings Z that are respectively
allocated to a switching matrix KV are set to a median counter reading of
the highest-possible counter reading. When, for example, the
highest-possible counter reading amounts to 1024, then the appertaining
counter readings during the set up of a connection can be set to a counter
reading of 512. For each forwarded message packet, the organization is
then undertaken such that the counter reading of the switching matrix KV
by way of which the appertaining message packet was transmitted is
incremented by a value that corresponds to the plurality of redundant
switching matrices KV in the packet switching equipment PVE, reduced by
one, whereas, accompanying this, the counter readings of the switching
matrices KV that have not transmitted the appertaining message packet are
decremented. When, for example, four switching matrices KV are provided in
a packet switching equipment PVE, then the counter reading of the
switching matrix KV that has transmitted the respective, forwarded message
packet is incremented by the value 3, whereas the counter readings of the
other switching matrices KV are respectively incremented by the value 1. A
switching matrix KV that has a respective lowest counter reading is
interpreted as being the respective slowest switching matrix KV. The
message packet respectively transmitted via the redundant switching
matrices KV have the next sequence number following the sequence number of
the most-recently transmitted message packet that proves faultless in the
check in the evaluation unit AWE and is accepted in the respective
evaluation unit AWE as the first of its message packet group is forwarded
to the serving line coming into consideration. In addition, each message
packet has a sequence number following the most-recently transmitted
message packet and that was faultlessly transmitted as the first of its
appertaining message packet group is forwarded to the serving line A
coming into consideration by the respective slowest switching matrix KV.
When, during the course of a connection, a counter in the example reaches
the lowest counter reading that can be represented by zero, then an outage
of the appertaining switching matrix KV can be assumed for the respective
virtual connection and measured can be initiated that are comprised in the
triggering of a malfunction alarm or therein that, in the forwarding of
following message packets for the virtual connection affected, a
correspondingly-reduced plurality of redundant switching matrices forms
the basis for updating the appertaining counter readings.
It can also be provided that, when all counters except one have the lowest
counter reading, an outage of the redundant transmission paths for the
respective virtual connection is assumed and forwarding each message
packet faultlessly transmitted via the switching matrix KV belonging to
the respective one counter that has a sequence number that follows the
sequence number of the most-recently transmitted message packet to the
serving line A coming into consideration is initiated. When only two
redundant switching matrices KV are provided in the packet switching
equipment PVE, then it is adequate to provide one counter for each virtual
connection, this counter being incremented for each message packet given
faultless transmission thereof via the one switching matrix KV as a first
of its message packet group and being decremented given a faultless
transmission via the other switching matrix. Given a counter reading that
is higher than the median counter reading, that switching matrix is the
respective fastest switching matrix KV and the other is the respective
slowest switching matrix KV, whereas, given a counter reading that lies
lower than the median counter reading, the associated switching matrix is
the respective slowest switching matrix KV and the other is the respective
fastest switching matrix KV. When the counter reading thereby reaches the
highest or the lowest counter reading, then an outage of the respective
switching matrix KV for the respective virtual connection can be assumed
and forwarding each message packet that was faultlessly transmitted via
the respective, remaining switching matrix KV as a first of its message
group to the serving line coming into consideration can be initiated.
A respective slowest switching matrix KV is identified with the information
V. For example, one bit can thus be provided for each switching matrix KV,
whereby the set bit can identify a respective slowest switching matrix.
When only two redundant switching matrices KV are provided in a packet
switching unit PVE, then one bit is adequate for the information V,
whereby the set bit can identify the one switching matrix KV as the
respective slowest switching matrix, in contrast whereto, the non-set bit
can identify the other switching matrix KV as the respective slowest
switching matrix. The information V is formed by evaluating the
call-associated counter readings Z. When the counter reading Z, as set
forth above, have been modified in the control device MP for a forwarded
message packet, the control device MP, by comparing the counter readings Z
belonging to the respective virtual connection, determined which has a
respective lowest counter reading and therefore identifies a respective
appertaining switching matrix KV as the respective slowest switching
matrix KV and set the information V assigned to such a switching matrix KV
in a corresponding manner. The information V, together with the counter
readings Z, the information W and the sequence number corresponding to the
packet just forwarded are input into the call-associated memory locations
of the memory SP. For each packet header that is accepted into the
selection circuit AS, the data belonging to the respective virtual
connection such as the stored sequence number, the counter reading Z, the
information W and the information V, are transferred into the control
device MP, whereby a decision as to how the respective message packet is
to be handled is made with reference to these appertaining data.
Although we have described our invention by reference to particular
illustrative embodiments thereof, many changes and modifications of the
invention may become apparent to those skilled in the art without
departing from the spirit and scope of the invention. We therefore intend
to include within the patent warranted hereon all such changes and
modifications as may reasonably and properly be included within the scope
of our contribution to the art.
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